1. Field of the Invention
The present invention relates to an exhaust purification catalyst warm-up system and method for warming up an exhaust purification catalyst disposed in an exhaust pipe of an internal combustion engine.
2. Description of the Related Art
An exhaust purification catalyst that removes harmful components, such as carbon monoxide (CO) or nitrogen oxides (NOx) from exhaust gas, via oxidation-reduction action, is provided in the exhaust system of an internal combustion engine. Because an exhaust purification catalyst is not sufficiently activated until it reaches at least a prescribed temperature (for example, 350° C.), it might not be possible to efficiently remove such harmful components from the exhaust immediately after the internal combustion engine is started, because the temperature of the catalyst is below the prescribed temperature.
Given the above, the Japanese patent application publication No. JP-A-2004-108248, for example, describes a secondary air supplying device for the purpose of quickly activating an exhaust purifying catalyst when an internal combustion engine is started, the apparatus supplies air to an exhaust pipe of the internal combustion engine and causes combustion of unburned fuel in the exhaust gas. With the secondary air supplying device it is possible to raise the temperature of the catalyst quickly, by promoting combustion of unburned components in the exhaust pipe to increase the temperature of the exhaust. Also, the above-noted secondary air supplying device extends the period of time during which air is supplied to the exhaust pipe longer, the lower is the atmospheric pressure. As a result, even when the atmospheric pressure is low, it is possible to raise the temperature of the catalyst to or above the activation temperature.
The Japanese patent application publication No. JP-A-2005-16396 describes a controller for an internal combustion engine that not only increases the intake air amount of an internal combustion engine in response to decreasing atmospheric pressure, but also injects fuel of an amount responsive to the intake air amount. According to this internal combustion engine controller, even when the atmospheric pressure is low, it is possible to quickly raise the temperature of the catalyst.
In the secondary air supplying device described in the Japanese patent application publication No. JP-A-2004-108248, however, by extending the period of time air is supplied to the exhaust pipe in response to decreasing atmospheric pressure, in other words, by extending the period of time of warm-up of the catalyst, the temperature is raised to at least the activation temperature. For this reason, although it is possible to raise the temperature of the catalyst to or over the activation temperature even when the atmospheric pressure is low, there was the problem of not being able to quickly activate the catalyst.
Also, when an exhaust purifying catalyst is warmed up, the controller for an internal combustion engine noted in the Japanese patent application publication No. JP-A-2005-16396 increases the intake air amount in response to a decrease in the atmospheric pressure, and injects an amount of fuel responsive to the intake air amount. For this reason, accompanying the increase in the intake air amount and the fuel injection amount, there is an increase in the output torque of the engine. As a result, when the engine is idling, the engine speed increases, and when the vehicle is running the vehicle accelerates to an extent that is noticeable by a driver.